There are plenty of side quests in Diablo 4, and some of them stand alone from the main story while others are vicariously related to it. The quest chain that involves an NPC named Sister Octavia is one of the latter. It's not part of the main plot, but it visits some common locations and drops a couple of big names.
There are three parts to this quest chain, and the player can continue with the game and skip them if they want, but there are some decent rewards and experience points to be had along with the experience of a great horror story. Thrilling horror and bloody mayhem are what Diablo 4 is all about, after all.
Diablo 4 has level scaling, so a character can start this quest whenever they want instead of waiting until a certain level. It's one way to keep with the game's theme of fighting evil and slaying demons as opposed to fetch quests or delivering messages.
Sister Octavia
Sister Octavia is the NPC involved in all three quests, and she can be found on one of the side streets of the city of Kyovashad. There seems to be some mystery as to her true identity and background, some of which is revealed in the course of the quest chain.
Despite her obvious connection to the Cathedral of Light, perhaps even a leadership rank, and what appears to be some intimate knowledge of Mother Prava's personal life, Octavia is acting outside of the strict rules set by the church. Her holy mission is a quiet one.
What makes Octavia unique among her peers is that she attempts to exorcise demons and rescue their human hosts. This is in direct opposition to the teachings that state those who are possessed must be burned. The denizens of Sanctuary have turned to her in desperation, hoping to save their possessed loved ones instead of seeing them executed.
Malady of The Soul
When the character first interacts with Sister Octavia she's standing with another person, Petr. It's Petr's son who has been possessed by a demon, and instead of just burning him, Petr hopes that Sister Octavia can successfully perform an exorcism.
- Speak with Octavia, agree to help, and follow her and Petr into the house.
- His little boy, Vata, is possessed, and the player's job is to protect Sister Octavia as she forces the demon out of the child.
- Touch the Holy Chalice on the ground to "place" it and begin the exorcism.
- There are two waves of enemies; the first is a group of smaller minions that attack the player, followed by the demon named Xul'goth, who isn't keen on leaving.
- This demon is essentially a mini-boss and is much tougher to defeat than the smaller demons.
- After Xul'goth is destroyed, Vata is restored and Sister Octavia meets you outside with a reward and mentions that she might need help again in the future.
Depths Of Despair
Leave Kyovashad and return to make the second quest appear. It starts in a similar way, with Octavia asking the player to help her as she performs another exercise. This time the subject is a man named Vasek, and his wife has enlisted Sister Octavia for help, but as the title of this quest implies things don't go according to plan.
- Join Octavia in the victim's house, but this time he hides upstairs and makes a break for it while everyone is looking for him in the basement.
- Pursue him into the Kyovashad Sewers, a mini-dungeon that opens up only for this quest.
- Place the Holy Chalice the same as the first quest.
- Demotath is the demon behind this possession, and he's a cut above Xul'goth from the previous fight.
- Despite Demotath's apparent defeat, Vasek explodes into a block of ice and is killed.
- Leave the dungeon and meet with Sister Octavia outside. The player gets a reward and thanks for her help, but she doesn't look very well.
The local Purvuyer of Curiosities, the vendor who accepts Obols as currency in return for unique gear, is located next to the entrance to the sewers. She is so horrified by the trail of gore left behind by the possessed Vasek that she's busy cowering, and won't be able to sell the player anything until the sewers are clear.
Faith In Blood
It turns out Demotath wasn't defeated. He possessed the body of Octavia instead, and it's up to the player to save her. This is by far the longest and most difficult quest of the three.
Kyovashad
- Leave and return to the city again. Petr will seek the player out with a letter from Octavia. She asks you to find her at Kvera's house.
- Upon arriving there, Octavia is barely lucid, but she tells the player they have to perform an exorcism on her, and they need a new Holy Chalice to do so.
Margrave
- Travel to Margrave and talk to Priest Matvey about a new chalice. He is kneeling by the grim pyre where most people who are possessed by demons are hanged to burn.
- Matvey is difficult, but he's afraid of Mother Prava, and mentioning her name scares him into giving the character a new chalice.
- The chalice must be consecrated with blood, Specifically, the Blood of Sinners, which can be found on the criminals and bandits hiding in the nearby wilderness.
Fractured Peaks
- Wander in the wilds and murder a few baddies, marked by red dots on the map, to fill the chalice. This fills automatically and can be tracked as the quest progresses.
- Return to Matvey to have the chalice consecrated. He sends the player back to Kyovashad with the Holy Chalice and asks that the player put a good word in for him with Prava.
Kyovashad
- Upon returning to Kyovashad, Petr is waiting outside the house. Speak to him, he'll impart that Octavia has taken a turn for the worst and has little time left.
- Follow him into the house and place the Holy Chalice on the marked spot on the floor to start the exorcism.
- The Baron of the Frozen Wastes sounds arrogant at first, but somehow Octavia is still fighting him and won't succumb to the same fate as Vasek.
- Demotath rises again, and upon his defeat, Octavia is winded but restored.
- Priest Matvey runs in, all pretense gone, but his attempt at a gotcha moment fails when he realizes the exorcism has been successful and the demon is dead.
- Meet Octavia outside and claim the rewards, which include Sister's Prayer Book in addition to the usual gold, experience, and local renown.
Diablo 4 is available on PC, PS4, PS5, Xbox One, and Xbox Series X.